Assuming that you believe that homosexuality is a sin (which is not set out in the bible as a sin), if all mankind are sinners (which we are according to the bible), then who cares which sin is committed by whom? God didn't put the commandments in order from 1 being minor and 10 being the worst.
Matthew 7:1-5
"Judge not, that ye be not judged. 2 For with what judgment ye judge, ye shall be judged: and with what measure ye mete, it shall be measured to you again. 3 And why beholdest thou the mote that is in thy brother's eye, but considerest not the beam that is in thine own eye? 4 Or how wilt thou say to thy brother, Let me pull out the mote out of thine eye; and, behold, a beam is in thine own eye? 5 Thou hypocrite, first cast out the beam out of thine own eye; and then shalt thou see clearly to cast out the mote out of thy brother's eye."
So from a christian point of view, all sinners are subject to original sin, and therefore should love one another so as not to be hypocrites.
As far as survival goes, a population will not die out due to homosexuality. It never has, and it never will, because heterosexuals have just as good a chance of being born as homosexuals. Considering that everyone who is alive has a mother, even if they are artificially inseminated. And furthermore, heterosexual couples can have as many kids as they can handle...so I wouldn't worry.
We are in more danger from violence than "sexual deviance"